Buffering

import { Grid } from 'cx/widgets';

Grid supports buffered rendering which dramatically improves performance with large datasets. Instead of rendering all rows, only visible rows plus a buffer are rendered, enabling smooth scrolling with thousands of records.

 <div controller={PageController}>
  <Grid
    records={m.records}
    keyField="id"
    buffered
    style="height: 400px"
    mod={["fixed-layout", "contain"]}
    cached
    selection={{ type: KeySelection, bind: m.selection }}
    columns={[
      {
        header: "#",
        align: "center",
        children: <div class="cxe-grid-row-number" />,
        defaultWidth: 70,
      },
      {
        header: { text: "Name", style: "width: 100%" },
        field: "fullName",
        sortable: true,
        resizable: true,
      },
      {
        header: "Continent",
        field: "continent",
        sortable: true,
        resizable: true,
        defaultWidth: 130,
      },
      {
        header: "Browser",
        field: "browser",
        sortable: true,
        resizable: true,
        defaultWidth: 100,
      },
      {
        header: "Visits",
        field: "visits",
        sortable: true,
        align: "right",
        resizable: true,
        defaultWidth: 70,
      },
    ]}
  />
</div> 
 class PageController extends Controller {
  onInit() {
    this.store.init(
      m.records,
      Array.from({ length: 5000 }, (_, i) => ({
        id: i + 1,
        fullName: names[i % 5],
        continent: continents[i % 5],
        browser: browsers[i % 5],
        visits: Math.floor(Math.random() * 100) + 1,
      })),
    );
  }
} 
 interface Record {
  id: number;
  fullName: string;
  continent: string;
  browser: string;
  visits: number;
}

interface PageModel {
  records: Record[];
  selection: number;
}

const m = createModel<PageModel>(); 
 import { createModel } from "cx/data";
import { Controller, KeySelection } from "cx/ui";
import { Grid } from "cx/widgets"; 

Name	Continent	Browser	Visits
Alice Johnson	North America	Chrome	13
Bob Smith	Europe	Firefox	19
Carol White	Asia	Safari	26
David Brown	South America	Edge	7
Eva Green	Africa	Opera	34
Alice Johnson	North America	Chrome	43
Bob Smith	Europe	Firefox	51
Carol White	Asia	Safari	36
David Brown	South America	Edge	92
Eva Green	Africa	Opera	49
Alice Johnson	North America	Chrome	48
Bob Smith	Europe	Firefox	78
Carol White	Asia	Safari	17
David Brown	South America	Edge	99
Eva Green	Africa	Opera	88
Alice Johnson	North America	Chrome	12
Bob Smith	Europe	Firefox	45
Carol White	Asia	Safari	85
David Brown	South America	Edge	99
Eva Green	Africa	Opera	4
Alice Johnson	North America	Chrome	69
Bob Smith	Europe	Firefox	55
Carol White	Asia	Safari	49
David Brown	South America	Edge	22
Eva Green	Africa	Opera	33
Alice Johnson	North America	Chrome	54
Bob Smith	Europe	Firefox	65
Carol White	Asia	Safari	57
David Brown	South America	Edge	92
Eva Green	Africa	Opera	45
Alice Johnson	North America	Chrome	64
Bob Smith	Europe	Firefox	92
Carol White	Asia	Safari	2
David Brown	South America	Edge	94
Eva Green	Africa	Opera	57
Alice Johnson	North America	Chrome	40
Bob Smith	Europe	Firefox	37
Carol White	Asia	Safari	94
David Brown	South America	Edge	15
Eva Green	Africa	Opera	5
Alice Johnson	North America	Chrome	76
Bob Smith	Europe	Firefox	5
Carol White	Asia	Safari	53
David Brown	South America	Edge	7
Eva Green	Africa	Opera	92
Alice Johnson	North America	Chrome	98
Bob Smith	Europe	Firefox	72
Carol White	Asia	Safari	42
David Brown	South America	Edge	36
Eva Green	Africa	Opera	57
Alice Johnson	North America	Chrome	88
Bob Smith	Europe	Firefox	61
Carol White	Asia	Safari	28
David Brown	South America	Edge	5
Eva Green	Africa	Opera	80
Alice Johnson	North America	Chrome	51
Bob Smith	Europe	Firefox	99
Carol White	Asia	Safari	76
David Brown	South America	Edge	89
Eva Green	Africa	Opera	66

This grid contains 5,000 rows but renders smoothly thanks to buffered mode. Try scrolling and sorting to see the performance.

How It Works

Enable buffered mode by setting the buffered property. The grid calculates which rows are visible and renders only those plus a configurable buffer for smooth scrolling.

<Grid
  records={m.records}
  buffered
  style="height: 400px"
  mod={["fixed-layout", "contain"]}
  cached
  columns={columns}
/>

For optimal performance, combine buffering with:

Fixed height - The grid needs a fixed height to calculate visible rows
mod="fixed-layout" - Uses CSS table-layout: fixed for faster rendering
mod="contain" - Adds CSS containment for better browser optimization
cached - Prevents row re-renders when unrelated store data changes

Row Numbers

Use the built-in cxe-grid-row-number class to display automatic row numbers:

{
  header: "#",
  defaultWidth: 50,
  children: <div class="cxe-grid-row-number" />
}

Configuration

Property	Type	Description
`buffered`	`boolean`	Enables buffered rendering mode.
`bufferSize`	`number`	Number of rows to render outside the visible area. Default is `60`.
`bufferStep`	`number`	Number of rows to add/remove when scrolling. Default is `15`.
`cached`	`boolean`	Prevents row re-renders when unrelated store data changes. Rows only update when their record data changes.
`lockColumnWidths`	`boolean`	Locks column widths to prevent layout shifts during scrolling.
`lockColumnWidthsRequiredRowCount`	`number`	Minimum number of rows required before column widths are locked.
`measureRowsOnScroll`	`boolean`	Re-measures row heights while scrolling. Useful for variable height rows.